PJE,
Thanks for sharing. We're taking a very similar approach, user space
with averaging for smoothing. We're using a moving average and use a
range from 20Hz to kHz at this point. What type of averaging techniques
are you using to smooth out your data?
We're working with Technologic Systems to try to customize our FPGA with
this capability. Hopefully, things will work out nicely. It sounds like
if you take the roll your own FPGA approach, you replace the existing
FPGA functionality that Technologic Sys provides...not god for us.
Thanks for sharing,
Ira
On Fri, 2006-08-04 at 00:45 +0000, PeterElliot wrote:
> Ira,
>
> My program is currently running in user space, and as the intention
> is to heve custom FPGA module, I've simply cross-referenced the
> velocity output from the quadrature to the speed the motor was
> commanded to spin at...
>
> I'm looking for changes in value rather than absolute values. I use a
> couple of simple averaging techniques to generate a smooth velocity
> trace - but I have the advantage of a lot more pulses per revolution.
>
> If you don't need the video you can create a custom FPGA application
> using the template Jesse Off placed on opencores.org. But my
> application needs the second SD card and Video, so paying Technologic
> Systems to produce the additional functionality is an economical way
> to go.
>
> It should be easy to implement a X4 counter rather than the X1
> counter, but the X1 has the advantage of having less noise induced
> jitter. I'm probably going to spec selectable X1 and X4 modes for the
> custom FPGA to investigate which gives the best results.
>
> I found an interesting webpage relating to quadrature and velocity at:
>
> http://zone.ni.com/devzone/conceptd.nsf/webmain/
> 492D39D15D27C5DF86256F3B004B9C1D
>
> Regards,
>
> PJE
>
> --- In "drrock77" <> wrote:
> >
> > PJE,
> >
> > Thanks for the info. I'd be really curious about using the x4
> > counting, I'd be interested in learning how one would modify the
> FPGA
> > to accomodate this.
> >
> > I've been using a similar approach for calculating the velocity. I'm
> > using the TC4 debug 4-bit timer as well. 983.04 kHz is what I read
> as
> > well. Unfortunately, I am not calculating RPM's correctly using this
> > appraoch. At least I this is what I think. I am verifying my
> > calculated velocity by measuring rotation with a non-contact optical
> > tachometer. Unfortunately, our encoder onlyhas 64 ticks per rev and
> > this is challenging to accurately calculate a velocity from.
> >
> > Did you perform any verifications on the T4 clock to ensure that
> your
> > timings are accurate/consistent? Did you develop a kernel module or
> > user space program to perform the velocity calculations.
> >
> > Our project is for a commercial application, so we may not be able
> to
> > use your code. I may be over simplifying thigs, but it should be
> > fairly straightforward to go from a x1 counter to a x4 counter.
> >
> > -Ira.
>
>
>
>
>
--
Ira Hoffman
Director of Research and Development
Freedom Sciences, LLC
610.585.7640
http://www.freedomsciences.com
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